House Republicans are homing in on a new line of attack against the administration’s health law enrollment numbers — “who’s paid” – and are now asking every insurance provider selling a plan through HealthCare.gov to tell them.

GOP lawmakers have been saying since the latest data showing 4.2 million people have picked plans through the online exchanges that the numbers could be inflated because an unknown proportion of those people have not yet paid premiums, which is necessary for their coverage to take effect. They’ve also hit the administration for its inability to say how many people had gained coverage after previously being uninsured, as opposed to switching their plans.

Federal officials say they don’t know how many people have paid their first month’s premiums and insurance companies are the ones who can answer that question. The House Energy and Commerce Committee appears to be taking the officials at their word, by firing off letters to every insurer offering coverage in the 36 states where the federal government is running the exchange.

The administration also says that HealthCare.gov only asks some people signing up for coverage if they previously had it and so it can’t provide accurate data about the full number of newly insured.

At the same time, though, they’ve pointed to McKinsey surveys (which we’ve reported on here and here) that found about 27% of 395 consumers surveyed in mid-February who enrolled in health-law coverage previously were uninsured, up from about 11% in an earlier survey covering consumers who had chosen coverage as of January.

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